Previously, various investigations into adhesion of toner particles to photoreceptors (so-called filming) have been conducted. For example, the method of adding a metallic soap to a developer layer to prevent toner particles from adhering and the method of adding an abrasive to a developer layer to scrape off adhered toner particles.
At present, progressive investigations are made of not only inorganic photoreceptors, but also organic photoreceptors, and the share of organic photoreceptors are increasingly broaden. The techniques of copying machines and printers have also progressed so as to use small-sized toner particles to attain high image quality.
As these techniques progress, a new problem is encountered in the techniques for preventing toner particles from adhering to photoreceptors.
Namely, although tolerable effects were realized by the use of the inorganic photoreceptors described above and the toner particles having a normal particle size in the conventional techniques, the use of the organic photoreceptors and the small-sized toner particles makes it impossible to obtain sufficient effects.
One reason for this is that the organic photoreceptors are soft in their surface compared to the inorganic photoreceptors and high in their reactivity, which is liable to cause the life thereof to be reduced.
When such organic photoreceptors are used, therefore, the use of so-called cleaning assistants such as metallic soaps, waxes and abrasives results in deterioration and scraping of the photoreceptors.
On the other hand, when the size of the toner particles is reduced, the problem arises that impaction to a carrier is liable to occur and the life is reduced. Furthermore, the small-sized toner particles are inferior to the toner particles having a normal particle size (10 to 20 .mu.m) in powder fluidity, and therefore, a large amount of fine inorganic particles are required to be used. In some cases, these fine inorganic particles contribute to filming.
For this reason, when the organic photoreceptor and the small-sized toner particles are used, there is no technique at present by which sufficient images can be obtained for a long period of time and which can prevent the toner particles from adhering to the photoreceptor to a satisfiable degree.